In the past, there has been known an exhaust gas purification device for an internal combustion engine that is provided with a NOx storage reduction catalyst to occlude and reduce NOx for purifying NOx components in an exhaust gas (see, for example, a first patent document (Japanese patent application laid-open No. 2000-240428), a second patent document (Japanese patent application laid-open No. H6-200740), a third patent document (Japanese patent application laid-open No. 2000-345831), and a fourth patent document (Japanese patent application laid-open No. S62-106826)). In such an exhaust gas purification device, a reducing agent is supplied to the NOx catalyst at appropriate times, so that NOx components contained in or held by the NOx catalyst are thereby reduced to be purified, thus regenerating the NOx catalyst.
Here, as methods for supplying the reducing agent to the NOx catalyst, in general, there are the following cases: that is, one case is that a liquid reducing agent is evaporated and then supplied in its gaseous state; and another case is that a liquid reducing agent is supplied in its liquid or droplet state. In the case of supplying a reducing agent in its gaseous state, there is a merit that a desired area can be put into a reducing atmosphere in a short period of time, but there is a demerit that it is impossible to reduce and purify the NOx held in the NOx catalyst unless the entire NOx catalyst has to be put into a reducing atmosphere. In contrast to this, in the case of supplying a reducing agent in its droplet state, there is a merit that it is possible to reduce the NOx held in the NOx catalyst by locally creating a reducing atmosphere without the need to put the entire NOx catalyst into a reducing atmosphere.
However, in the case of supplying a droplet-like reducing agent, there arises a problem that it is difficult to locally create a reducing atmosphere, so it becomes difficult to reduce and purify the NOx held in the NOx catalyst to a satisfactory extent. Here, note that if the amount of reducing agent supplied is too large, it is released or emitted to the atmosphere as it is without being adhered to the NOx catalyst, so the amount of the reducing agent to be supplied must be limited.